The plane took off at 1 AM EDT today (a little before 7 AM Swiss time) from the Payerne airfield in clear blue skies.
By mid-morning it was cruising at around 10,000 feet. Pilot Andre Borschberg, who has been conducting interviews with journalists from the cockpit, will slowly ascend to 28,000 feet -- taking time to adjust to the colder temperatures and lower oxygen levels he will encounter there -- before deciding by tonight (or 2 PM EDT) whether to continue flying in darkness.
From the plane's Web site:
At that point he will still be flying purely on solar energy, not on the batteries charged up by the wings’ 10,748 solar cells. But approximately an hour later, the angle of the sun will be too low for him to maintain his altitude on solar power alone. The technical term is that he will “lose energy balance.”
Not wanting to expend any battery power until absolutely necessary, he’ll then start a very shallow glide downward, using potential energy rather than his battery power to stay aloft.
This is the plane's third test flight, and it's critical to seeing whether the aircraft is capable of flying around the world, which the organizers of the project -- including the balloonist Bertrand Piccard -- want to do by 2012.
Wired reports the plane as having four, 10-horsepower electric motors with a cruise speed of roughly 40 miles per hour (70 km/h), 11,628 solar cells to power the motors and charge polymer lithium batteries, and a wingspan of 208 feet (63.40 meters) -- as wide as a jumbo jet, but with a weight of only 3,520 pounds (1,600 kilograms), about the same as a car.
You can follow the flight in progress and see features of the plane here.
Here, meanwhile, is a short video from the BBC that includes a tour of the plane's cockpit.
This post was originally published on Smartplanet.com